Trichomonas vaginalis is the etiologic agent of the most common non-viral sexually transmitted infection worldwide and is the most prevalent parasite found in the U.S. population. Increased transmission of HIV in women chronically infected with this parasite and the recent increase in the appearance of drug resistant strains warrant a better understanding of the biology of this understudied organism. The proposed study aims to provide knowledge on the biogenesis and biochemistry of an unusual organelle, the hydrogenosome, that is present in T. vaginalis, but absent in its human host. This organelle is the target of the only drug licensed for therapy for Trichomoniasis, metronidazole. Our previous research on hydrogenosomes has led to a series of observations that indicate common properties are shared by hydrogenosomes and mitochondria, the equivalent organelle in host cells. However, distinct differences, which might be exploited for drug design, have also been discovered. In addition to its medical importance, knowledge of the protein composition of the hydrogenosome and phylogenetic analyses of its components should help clarify how novel cellular structures and functions were acquired in early eukaryotes and assist in understanding how energy-generating organelles evolved in the first eukaryotic cells 2-3 billion years ago. To this end, our overall goals are to understand properties of biogenesis and evolution of this organelle and establish its relationship to mitochondria. Our specific aims are: (1) To elucidate the functions of hydrogenosomal membrane proteins and examine their possible roles in organelle biogenesis; (2) To identify hydrogenosomal pre-sequence peptidases, using biochemical and bioinformatics approaches, and compare these with mitochondrial counterparts and (3) To begin to define the proteome of T. vaginalis hydrogenosomes. These studies will increase our understanding of the biogenesis, evolution and metabolic properties of organelles in eukaryotic cells, in addition to providing important new information on a novel organelle in this parasite.